Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $95.34   9.624%   $104.5155   $104.52   $104.50   $104.50  
  Purchase #2 $228.98   5.708%   $242.0502   $242.05   $242.05   $242.10  
  Purchase #3 $173.51   13.754%   $197.3746   $197.37   $197.35   $197.40  
  Purchase #4 $18.89   5.685%   $19.9639   $19.96   $19.95   $20.00  
  Purchase #5 $60.93   5.137%   $64.06   $64.06   $64.05   $64.10  
  Purchase #6 $96.53   3.115%   $99.5369   $99.54   $99.55   $99.50  
  Purchase #7 $70.38   4.776%   $73.7413   $73.74   $73.75   $73.70  
  7 purchase totals = $744.56       $801.2424   $801.24   $801.20   $801.30